Rheostat



April 27,1926.'

E. R. STOEKLE RHEOSTAT Filed May 5, 1924 nur INM/WOR Patented Apr. 27,1926.

UNITED STATES ERWIN 1t.y STOEKLE, OF MILWAUKEE, WISCONSIN.

RHEOSTAT.

implication mea May 5,

To all whom t may concern.'

Be it known, that I, ERWIN R. STOEKLE,

a citizen of the United States, residing at Milwaukee, in the county ofMilwaukee and State cf lVisconsin, have invented new and usefulImprovements in Rheostats, of which the following is a full, clear,concise, and exact description,- reference being had to theaccompanyingdrawings, forming a part of this specification.

This' invention relates to improvements in the construction ofelectrical resistance devices particularly rheostats for the control ofan electric current. l

In rheostats in which the variably. contacting element bears directly onthe turns of wire of the electrical resistor a common difficulty arisesin theloosening of these turns of wire upon theirsupport, due to thedifferential expansion of the ywire and its support caused bythe heatgenerated by the electrical current. This loosening of the` turns of theresistor causes them to move and touch one another when the contactingelement is' moved, thereby causing erraticl changes in the resistance.

. One object of this invention is to provide a resistance device inwhich the wire constituting the resistance element is firmly held inposition.

Another obJect is to provide a rheostat structure i-n which the wireelements constituting the resistor are firmly clamped betweenelectrically insulating and slightly yielding surfaces, so that eachelement will besomewhat embedded in said insulating surfaces, and thusheld in insulated relation with its neighboring elements.

Another purpose of this'invention is to provide an effective andeasilyassembled structure for accomplishing the above ob jects. Anotherobject is to provide a rheostat structure in which `effective cooling ofthe resistor is accomplished by conduction and radiation of thegenerated heat.v

Other objects and novel features of this 'improved resistance devicewill be apparent from the following description and drawings of Figs. 1to 6. l

Figure 1 shows a perspective view of a preferred form. of the resistancedevice. Figure 2 shows across sectional View of the structure of Fig. 1.

Figures 3 and 4 show' respectively the 1924. serial No. 71,1,1-98.

groove formed by the external cylindricall shell or cup 2 and theinternal cylindrical member 3. The resistor is insulated from thesemetal cups by means of the insulating strips 5 and 6 and the insulatingWasher 4. These strips are preferably of a slightly yielding materialsuch ,as asbestos paper or the like so that the wire of the resistancelelement may become partially embedded therein. e Y

The external and `internal cylindrical members are shown as made ofmetal a1- tho'ugh either or both may obviously be made of someinsulatingmaterial in which case lthe corresponding insulating strips may beomitted. A good alternative construction is to make thevexternal shellof metal and the internal member a cylinder ofmoulded insulatingmaterial.

The terminal posts Y Figs. 1, 3 and 4 serve to establish electricalconnection with one end of the wire of the resistor as shown vin Fig. 3,and also for connecting to the metal cups as shown in Fig 4. In Fig. 3the terminal screw 7 is shown riveted at 26 to the insulating core 25upon which the resistance wire 28 is wound. The end of this wire' isshown bound under the nut 27. In Fig. 4 the terminal 8 is shown -with athreaded portion extending throughV the metal cup 2 and fastened theretoby means of a nut 29.

Referring again to the Fig. 2 the threaded hollow bushing 9 extendssubstantially centrally through the metal cups. This bushing incooperation with the shoulder l10 and the nut 11 serves to hold themetal cup 3 firmly within the resistor. The inner cylindrical surface ofthe cup 2 and the` outer cylindrical surface of the cup 3 may be formedslightly conical as shown, so that as these cups are drawn together bymeans 7 and 8, shown in -of the nut 11 a very considerable radial'.

. This will result in partially embedding the wires of the resistor inthe insulating strips whereby they will be firmly held in ,insulatedrelation `with respect to each other.

An enlarged sectional view of the manner in which the wires of theresistor are partially embedded in the adjacent insulating surfaces isshown in the Fig. 5. This figure shows a portion 19 of the core uponwhich the resistance -wire 2O is wound; and the adjacent insulatingsurfaces 21 and 22. A portion of the walls of the external and internalmembers are shown at 23 and 24: respectively. The radial'pressureexerted betw'een the wires and the adjacent insulating surfaces causespart of the insulation to extend between neighboring wires as shown,whereby they are prevented from making contact with one another. l

Another method of holding lthe wires firmly in position is to have onlythe inner member conical, in which case the maximum radial pressure isexerted on the resistor near its upper edge only.

Referring again to the Fig. 2 the shaft 12 extending through the,hol1owbushing 9 has fastened to one end the operating knob 13 and the pointer14. The collar 15 is -fastened to the other end of this shaft by meansof the set screw 16, and carries the contact arm 17 `which bears 'uponthe resistor at its exposed edge. v

The operation of the device shown in Figures land 2 is as follows:

An electrical current entering the terminal 7 (Fig. l) traverses theresistor to the point in contact with the contact arm. It then passesalong the contact arm to the shaft and to the metal cups, which' are inelectrical connection with the terminal 8. In the construction in whichthe members` are made of -insulating material, it is necessary toprovide a metallic connection from the contact arm to the terminal 8.The rotation of the contact arm 17 by means of the knob 13 obviouslvaries theresistance between the termina s 7 and 8. The turns of theresistor being firmly embedded in the manner described above will beprevented from moving under' the sliding friction ofthe contact shoe.The resistance wire being separated from the metal cups by only a thinlayer of. electrical insulation, the heat generated in these wires' isreadily conducted to these cups and radiated therefrom.

`The Fig. 6 shows another structure for U ing a cyhndrical shellwith-aconical inner achieving the samefirm anchoragel of the resistance wire.In this ligure the moulded insulating base 30 has tHe resistor'v 31mounted about its cylindrical surface. An insulating strip 32 isplacedadjacent the turnsof the resistor and ametal'band 33 Vhold .thewires of the resistor in insulated relation with respect to each otherin a `manner similar to that described for the Figs. 1 and 2; and alsothe insulating base provides a convenient mounting for the terminalposts as shown at 34. The metal strip 39 serves to establish electricalconnection between the terminal .34C and the movable contact arm 37. Theshaft 35, knob 36, and contact arm 37, of this figure are arranged inthe manner shown and function in the same-way as described f or Figs. 1and 2.

What I claim as new and desire to secure by Letters Patent is:

1. An electrical resist-ance device comprising a disc with a fiangededge.; a second disc with a flanged edge of smaller diameter than saidfirst mentioned disc; and a resistance element held in the annulargroove formed by the iianged edges of said discs and electricallyinsulated from said discs, and suitable terminals for making electricalconnection with said resistance element.

2. An electrical resistance device comprising an external cylindricalshell; a resistorcircularly disposed within said shell; suitableterminals for said resistor; insulating sur-.

faces adjacent the inner and the outer circumferential surfaces of saidresistor; an

internal member having a slightly conical 3. An electrical resistancedevice comprisving a cylindrical cup shaped member; a

insulating surfaces of slightly yielding character adjacent saidresistor; means for drawing and holding said inner' member tightlywithinv said resistor whereby a radial compression is exerted upon saidresistor and the wire elements thereof'are partially embedded in andfirmly held. by said insulating surfaces.

circumferential surface; a resistor .disposed within said'shell;suitable terminalsfor said resistor; a second cylindrical member havinga conical surface substantially-parallel 'to the inner conical surfaceof said first` nien-v .4. An electrical resistance ldevicecomprisassasse tioned shell; insulatin strips adjacent Said conicalsurfaces; and means for firmly pressing said inner member and itsassocie ated insulating strip within said resistor,

whereby la radial compression is exerted upon said `resistor and thewire elements thereof are partially embedded in and firmly held inposltion by' said insulating strips.

5. An electrical resistance device comprising a circularly disposedrisistor; suitable terminals for -said resistor; insulating surfacesadjacent the inner and the outer circumferential surfaces of saidresistor; a vcylindrical shell Within Vwhich said resistor is mounted; asecond cylindrical member adapted to be rml pressed inside said re-.sistor whereb sai resistorisv firmly compressed and eldl between itsadjacent insulating surfaces.` l

6. An electrical resistance device comprising a plurality of cylindricalshells of var ing diameters, co-axially mounted one Witiiin the other, aresistance clement firmly clamped in the annular groove formed 'by saidc lindrical shells' and electricallyfin sulate therefrom, and suitableterminals for establishing electrical connection with said resistanceelement. s

7. An electrical resistance devicecomprising a cylindrical shell; a'resistor mounted within said shell and insulated therefrom;

a terminal connected to 'one end of said'V resistor; a secondcylindrical shell firmly pressed within said resistor 'and insulatedtherefrom; a hollow bushing externally threaded and provided with ashoulder and a nut for firmly holding said shellsI together; a shaftrotatably extending through said bushing; a contact member attached toone end of said shaft and adapted'. to make a slidinncontactwith saidresistor; an operating `and 1tsassociated contact member; and a ob forrotating said 'shaft terminal for establishin electrical connection tosaid contact mem er.

8. An electrical resistance device comprisding' a circularly disposedresistor; suitable terminals for said resistor; an external-band'surrounding said resistor and insulated therefrom; anl internalcylinder insulated from said resistor and Vadapted to be' firmly pressedinto position2 whereby said resistor is subjected to a radialcompression and the elements thereof are firmly held in lace. Y,

9. An electrical resistance device comprising a cylindrical insulatingbase; a resistor mounted on the cylindrical surface of saidbase;suitable terminals for said resistor; an insulating surfaceadjacent the outer surface of vsaid resistor; a cylindrical membersurrounding said 'insulating surface and adapted to exert a pressurethereon, whereby the l `upon said resistor; a contact arm forestablishing a vsliding contact on the wire of said resistor; a terminalfor establishing electrical oonnection'to said contact arm; and

suitable means for rotating said contact arm into a variable position ofcontact on said resistor. .l

In witness whereof, 1 have hereunto subscribed my name.-

ERwN R. sToEKLE,"

